This invention relates to a liquid fuel cell, and more particularly to a method of producing an electrode useful as the fuel electrode or anode of the fuel cell.
Known fuel cells include liquid fuel cells that utilize an acidic solution as electrolyte and an organic liquid compound such as methanol or formic acid as fuel. It is conventional to use a noble metal such as platinum as the electrode material for the anode of a liquid fuel cell of this type.
Concerning a fuel cell electrode formed of a plate of platinum or an alternative noble metal, U.S. Pat. No. 4,309,315 shows a method of activating the surfaces of the platinum plate and maintaining the activated state. In this method, the activation is accomplished by a known technique such as an electrochemical oxidation and reduction process which has the effect of changing the arrangement of platinum atoms in a surface region of the electrode plate to a partially dislocated and unstable state. The platinum surface exhibits a high activity so long as it remains in such an unstable state. Following the activating process, a relatively small amount of another metal such as tin is deposited on the activated platinum plate, by electrodeposition for example, in order that a portion of the newly deposited base metal may intrude into the vacancies in the atom arrangement of platinum in the unstable and activated state. The base metal such as tin deposited in such a manner serves the purpose of maintaining the platinum surface in the activated state. As will be understood, it is a requirement that the deposition of a base metal such as tin be accomplished in a short time before the platinum surface reverts to the stable state. This requirement can be met because the electrode body is a solid metal plate having smooth surfaces and, hence, the solution containing tin ions used in the electrodeposition process can rapidly diffuse onto the entire area of the electrode surfaces.
From an economical point of view, it is unfavorable to use an expensive noble metal as the structural material of the electrode. Accordingly, a different type of electrodes for liquid fuel cells are under development based on the thought of using a porous body of an inexpensive and electrically conductive material such as carbon and coating and impregnating the porous body with a small amount of noble metal such as platinum. However, in the production of an electrode of this type it is difficult to effectively utilize the technique of the above quoted U.S. patent to maintain platinum on the electrode body in a highly activated state. The reason is that at the electrodeposition of a base metal such as tin, the solution containing the metal ions does not easily arrive at the platinum surfaces in the micropores in the electrode body and, therefore, a desired manner of deposition of the metal such as tin on the platinum surfaces can hardly be accomplished within a short time during which the platinum surfaces remain in the activated state.